The objective of this project is to understand the mechanisms by which middle ear cholesteatoma erodes bone and damages the inner ear. The long-term goal is to develop pharmacological methods to control tissue damage due to cholesteatoma, thereby avoiding ablative surgery. First, the mechanism of bone resorption will be studied. Bone resorption in cholesteatoma is primarily due to the action of multinucleated osteoclasts but mononuclear cells may also erode bone. The bone of gerbils will be pre-labeled with Ca45 or (H3)tetracycline; at 80 days, cholesteatomas will be induced. The animals will be killed when bone resorption occurs. Undecalcified tissue sections will be autoradiographed. Cells actively resorbing bone will be labeled; the relative contribution of each cell type to bone destruction will be inferred from the number of cells labeled. Prior to their sacrifice, these labeled animals will be monitored for urinary excretion of Ca45 or H3. An increase in excreted isotope may be an accurate in vivo reflection of bone resorption. The human and gerbilline osteoclasts responsible for bone resorption in cholesteatoma will also be removed and placed into short-term cultures. The cytoplasmic activity and spreading will be assessed using video lapse photography. The effects of prostaglandins upon the cytoplasmic activity of these osteoclasts will be compared to the effects of the same substances upon physiological osteoclasts. Additionally, the presence of various prostaglandins in cholesteatoma will be measured using radiochromatography of (C14) arachidonic acid metabolites. Since preliminary studies have shown that gerbils with middle ear cholesteatomas have marked hair cell loss, we will evaluate cochlear hair cell loss in age matched gerbils with and without cholesteatomas. The cochlea will be evaluated using air and bone conducted auditory brainstem responses, scanning electron microscopy of hair cells and transmission electron microscopy of hair cells and the stria vascularis.